The present invention relates to a method for cephalometric imaging using an apparatus which comprises an X-ray source, a line detector camera equipped with a digital detector, which line detector camera is located to a position far away from the X-ray source for carrying out cephalometric imaging while the slot of the line detector camera is substantially vertical, whereby in cephalometric imaging, an X-ray beam located substantially on the vertical plane is directed from the X-ray source through the object being imaged, and the X-ray source is at the same time turned about the rotation centre located between the X-ray source and the line detector camera in order to scan the object being imaged in the horizontal direction, whereby the line detector camera is moved during the scanning movement in such a way that the ray beam meets the slot of the line detector camera. The publication U.S. Pat. No. 5,511,106 discloses this type of scanning method for cephalometric imaging.
When cephalometric imaging is carried out in the manner described in the preamble, the vertical ratio of enlargement remains the same as without the scanning movement, but the horizontal ratio of enlargement, on the other hand, changes because the rotation centre changes into the effective focal spot instead of the focal spot of the X-ray source. Accordingly, the object of the present invention is to provide a method by means of which the ratios of enlargement in cephalometric imaging can be maintained the same in the vertical and horizontal directions in cephalometric imaging, which is carried out by means of the turning movement taking place about the rotation centre of the X-ray source. A further object is to provide a method which can be implemented by using existing panoramic X-ray imaging apparatuses, which already comprise the means needed to perform the required movements. To achieve this object, the method relating to the invention is characterised in that in the method, the effective focal spot is transferred from the rotation centre to the focal spot of the X-ray source by transferring the rotation centre by means of a transverse linear movement with respect to the ray beam